I suspect "per car produced" has a lot more to do with Toyota producing higher volume than Tesla. At least according to the stuff that's been popularized and written about, the Toyota Production System de-emphasizes automation. The rationale being that until you've refined the manufacturing process through experience, you don't know which steps to automate.

Think of it this way: if you rely upon robots too much, you're making a huge bet that you can design the manufacturing process from scratch and basically get it right the first time. If you get something wrong, it's going to be expensive to go back and improve it because you need to rework all of the automation. Conversely, if you design a less automated manufacturing process, more of the work is done by human beings, who are typically smarter and more adaptable than robots. That way, if you come up with process improvements later on, you can just teach it to the humans. Better yet, the humans themselves can think of their own process improvements.

At any rate, Toyota produces millions of cars in the United States on an annual basis; clearly the cost of American labor isn't a problem for them.